1. Technical Field of the Invention
The present invention relates to devices known as throat bushings, which are commonly used to improve the environment of seal packing positioned at the entrance to a seal cavity in rotating fluid equipment.
2. Description of the Prior Art
Sealing equipment of various types is used in pumps in a variety of different industries for a variety of different purposes and applications. In order for the sealing equipment, which includes packing, bushing and mechanical seals, to operate continuously without premature failure its environment must be free from contaminants. In order for this to be the case, a number of different techniques and accessories are used, however this patent is limited to accessories that are used with packing, called throat bushing.
P.C.T. Patent Application Publication No. WO 2007/129080 A2 teaches that one such solution for this issue is called the SpiralTrac seal, which is an annular bushing which is placed at the entrance to a seal cavity of a pump, the cavity being defined by a portion of the pump housing, a shift that extends through the cavity, and a means for sealing a cavity itself. The sealing may take the form of a mechanical seal or packing material. The bushing includes a tapered central surface, which has a spiral groove formed in its wall and which extends from adjacent to the outer surface of the bushing towards the cavity entrance. The spiral groove decreases in diameter down to the innermost diameter of the bushing, which defines a small angular gap around the shaft.
As the shaft rotates, any particulate material that enters the seal cavity during operation of the pump will be centrifugally forced into the spiral groove and will flow towards the gap around the shaft. The particulate material is then forced outwardly through the gap to the exterior of the seal cavity.
In P.C.T. Patent Application Publication No. WO 2007/129080 A2, an apparatus is described that overcomes the disadvantages of the SpiralTrac product by having more than one groove ensuring that should the contaminants build up in such a way that the groove is rendered impassable there is another that will ensure the flow of contaminants is maintained. The superior design also includes a groove, which is rotated in clockwise direction and another which is in anticlockwise direction, thereby allowing the product to operate irrespective of the direction of shaft rotation.
Through manufacturing trials it has be subsequently learned that this construction, although superior to the SpiralTrac design, is very costly to manufacture. This is due to the nature of the grooves and vanes requiring complex geometry to be machined onto the inner surface of the product and so meaning that jigging must be manufactured for each size variant which allows the product to be secured on a machine post splitting.